squiggle/src/utility/GuesstimatorLibrary.js

import { Guesstimator } from '@foretold/guesstimator';
import { Samples } from '@foretold/cdf';
import _ from 'lodash';

/**
 *
 * @param {number} minValue
 * @param {number} maxValue
 * @returns {string}
 */
const minMaxRatio = (minValue, maxValue) => {
  if (minValue === 0 || maxValue === 0) {
    return 'SMALL';
  }
  const ratio = maxValue / minValue;
  if (ratio < 100000) {
    return 'SMALL';
  } else if (ratio < 10000000) {
    return 'MEDIUM';
  } else {
    return 'LARGE';
  }
};

/**
 * @param samples
 * @return {string}
 */
const ratioSize = samples => {
  samples.sort();
  const minValue = samples.getPercentile(2);
  const maxValue = samples.getPercentile(98);
  return minMaxRatio(minValue, maxValue);
};


const toPdf = (values, sampleCount, min, max) => {
  let duplicateSamples = _(values).groupBy().pickBy(x => x.length > 1).keys().value();
  let totalLength = _.size(values);
  let frequencies = duplicateSamples.map(s => ({value: parseFloat(s), percentage: totalLength/_(values).filter(x => x ==s).size()}));
  let continuousSamples = _.difference(values, frequencies.map(f => f.value));
  const samples = new Samples(continuousSamples);

  const ratioSize$ = ratioSize(samples);
  const width = ratioSize$ === 'SMALL' ? 20 : 1;

  const cdf = samples.toCdf({ size: sampleCount, width, min, max });
  return {continuous:{ys:cdf.ys, xs:cdf.xs}, discrete: {xs: frequencies.map(f => f.value), ys: frequencies.map(f => f.percentage)}};
};

let run = (text, sampleCount, inputs=[], min=false, max=false) => {
    let [_error, item] = Guesstimator.parse({ text: "=" + text });
    const { parsedInput } = item;
    const { guesstimateType } = parsedInput;

    const guesstimator = new Guesstimator({ parsedInput });
    const value = guesstimator.sample(
      sampleCount,
      inputs,
    );
    const samplerType = guesstimator.samplerType();

    const values = _.filter(value.values, _.isFinite);

    let update;
    if (values.length === 0) {
      update = {xs: [], ys: []};
    } else if (values.length === 1) {
      update = {xs: [], ys: []};
    } else {
      update = toPdf(values, sampleCount, min, max);
    }
    return update;
}

module.exports = {
  run,
};